The area postrema (AP) in the caudal 4th ventricular floor is unique, highly vascular without blood/brain or /CSF barrier. In addition to its function as the vomiting centre, several other important functions are: part of the circumventricular organs for vasomotor and angiotensin II regulation; a role in neuromyelitis optica related to aquaporin-4; contributor to fetal and postnatal somatic growth. Functions are immature at birth.

The purpose of this study was to demonstrate AP neuronal/synaptic/glial maturation in normal fetuses and 3 AP tumours. Transverse sections of the caudal 4th ventricle of 18 normal human fetal brains at autopsy, 6 to 40 weeks were examined; also 3 infants 3-18mos; 2 children. A battery of immunocytochemical neuronal and glial markers: MAP2; calretinin; synaptophysin; vimentin; nestin; GFAP; S-100β protein; were applied to paraffin sections. Two children with AP tumours and one with neurocutaneous melanocytosis, all with pernicious vomiting, were studied. In normal fetuses, AP neurons exhibited cytological maturity and well-formed synaptic circuitry by 14wk gestation. Size/volume increase was disproportionately greater than brainstem growth in 2nd and 3rd trimesters and postnatally. Astrocytes co-expressed vimentin/GFAP but glia were best demonstrated by S-100β protein. Ependyma over the AP in fetuses is simple cuboidal, adjacent to pseudostratified columnar of the 4th ventricular floor. Melanocytes infiltrated AP in the toddler with pernicious vomiting; 2 children had primary AP pilocytic astrocytomas. Though AP is cytologically mature by 14wk, growth increases and functions mature into the postnatal months. We recommend that AP neuropathology include synaptophysin and S-100β at autopsy if AP dysfunction suspected.